A variety of systems applying a heat pump employing CO2 as a refrigerant and utilizing natural water such as well water, underground water, etc. as a heat source or cold source to air-conditioning or hot-water supplying, has been proposed in the past.
For example, in Japanese Laid-Open Patent Application Publication No. 8-247496 (prior art 1) is disclosed a system utilizing a heat pump which performs snow melting, room heating, room cooling, etc. utilizing underground water as a heat source or cold source. In the system, pumped-up underground water is used directly to melt snow, and the water after used to melt snow is utilized as a heat source for the evaporator of a heat pump, then the water after use is returned to a well.
In Japanese Laid-Open Patent Application Publications No. 2002-54856 and (prior art 2) and No. 2002-54857 (prior art 3) are disclosed systems in which a heat pump utilizing underground water is applied for the purpose of air conditioning and hot-water supplying for residential houses. In the system, switching between cooling and heating cycle is performed by a four-way valve.
In Japanese Laid-Open Patent Application Publication No. 2002-146852 (prior art 4) is disclosed a system for performing air conditioning, etc. utilizing underground water as a heat source or cold source.
However, these prior arts have such problems that there are technical problems to be solved when applying to practical use, that a large-scaled facility is required, and that high efficiency is not expected, and they are not put into practical use in the present circumstances.